The two formulas that matter
A monitor that checks every T minutes cannot see an outage before the next check after it begins. If an outage starts at a random moment:
worst-case delay to detect = T (+ confirmation time)
average delay to detect = T / 2 (+ confirmation time)So a 5-minute interval means you learn of an outage, on average, 2.5 minutes after it starts, and in the worst case after 5. With a confirming check from a second region or consecutive failures required, add that time.
The cost side is the number of checks:
checks per month per location = 43,200 / T (30 days, T in minutes)One-minute checks mean 43,200 requests a month per location; five-minute checks, 8,640; fifteen-minute checks, 2,880. For a small site, load is negligible. For a portfolio of 100 sites checked from two regions every minute it is 8.64 million requests a month, which is why some vendors limit the shortest interval by plan.
An outage shorter than the interval can be missed completely. A 90-second restart is invisible to a five-minute check unless it happens to coincide with one. That is a feature for noise and a blind spot for the client who loses sales in those 90 seconds.
Matching the interval to the client
There is no universal figure. Work from the cost of downtime.
| Site type | What a minute of downtime costs | Typical choice |
|---|---|---|
| Brochure site, low traffic | Little; visitors come back | 5 minutes is enough; 1 minute if cheap |
| Lead generation with paid campaigns | Ad spend burns while the page is down | 1 minute during campaigns |
| Shop | Orders lost, abandoned carts | 1 minute, with a check of the cart or checkout page |
| Booking, appointments | Lost bookings, phone calls | 1 minute |
| Landing page for an event | Everything on one day | 1 minute, with a person on call that day |
| Internal tools | Staff wait | 5 minutes |
The estimate does not have to be precise. If the client earns 600 a day online, one lost minute is about 0.4 on average. The delay matters less than the question “how long until a human acts”.
Detection is not the same as response
A one-minute interval is useless if the alert goes to an inbox read at 9 a.m. Three delays add up:
- Detection: up to the interval, plus confirmation.
- Notification: how fast the channel delivers (email can be slow; chat and webhooks are faster).
- Response: how long before a person looks.
For many agencies the third dominates. Moving from five-minute to one-minute checks shaves two minutes at best, while agreeing who responds out of hours saves hours. Decide the response first, then the interval.
Intervals and false alarms
A shorter interval gives more chances for a false failure. If a location wrongly fails 0.2 percent of checks, one-minute checks produce more false failures than five-minute checks, in proportion. That is where confirmation helps: requiring a second region to agree removes most of them, and it is why short intervals and confirmation go together. See Two-region confirmation and false alarms.
Different checks, different intervals
Not everything needs checking every minute.
- Page availability: every minute, or every five.
- TLS certificate: the expiry date changes once a day at most; checking hourly is plenty. The shortest certificate lifetimes are measured in weeks (see SSL certificate expiry).
- DNS records: every few minutes, or whenever the page is checked, if the tool records them with the check.
- Domain expiry: daily.
- robots.txt and meta robots: with the page check, or every few minutes. Change is rare; impact is large.
- Scheduled jobs: by their own period (see Heartbeat and cron job monitoring).
What the vendors say
Intervals differ by tool and by plan. Oh Dear’s documentation, for example, says uptime checks happen every minute from the primary location (read on 2026-10-26). Other tools offer 30-second checks or faster on higher plans. Read the plan details before assuming; this page does not rank them.
A sensible default for an agency portfolio
- One-minute page checks for sites that make money or run campaigns.
- Five-minute checks for brochure sites, if the tool charges for the shorter interval.
- Confirmation from a second region on all of them.
- A named responder and a stated response time in the care plan.
- A monthly look at the alerts: how many were real, how many were noise, how long each took to resolve. Adjust the interval and confirmation from that record.
How Beamfar helps
Beamfar checks every minute on the paid plans (every 30 seconds on Team and up, for the checks you set to it) and every 5 minutes on the Free plan, from every enabled region, and calls a site down only when two regions agree. The monthly report shows the incidents and the method behind the uptime figure. You do not choose a slower interval to save cost, so the decision left to you is who responds and how fast.
Questions
How long does it take to detect an outage with a 5-minute interval?
On average 2.5 minutes after it starts, and at most 5 minutes, plus any time the monitor needs to confirm the failure. Outages shorter than the interval can be missed.
How many checks does a monitor make in a month?
43,200 divided by the interval in minutes, per location, for a 30-day month. One-minute checks make 43,200 and five-minute checks make 8,640.
Is a one-minute interval always better?
It shortens detection, and it gives more chances of a false failure, so pair it with confirmation from a second location. It matters less than agreeing who responds, and how fast.
Should the SSL certificate be checked every minute?
No. Expiry changes slowly, so hourly or even daily is enough for the date. A replaced certificate is worth noticing quickly, which is why many tools read it with each page check.
Sources
Read on . Standards and vendor pages change; confirm the current text before you rely on it.